Heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. For heat assisted magnetic recording (HAMR) a tightly confined, high power laser light spot is used to heat a portion of the recording medium to substantially reduce the coercivity of the heated portion. Then the heated portion is subjected to a magnetic field that sets the direction of magnetization of the heated portion. In this manner the coercivity of the medium at ambient temperature can be much higher than the coercivity during recording, thereby enabling stability of the recorded bits at much higher storage densities and with much smaller bit cells.
In heat assisted magnetic recording, information bits are recorded on a storage layer at elevated temperatures, and the heated area in the storage layer determines the data bit dimension. Focusing devices such as a solid immersion lens (SIL) or a solid immersion mirror (SIM) can focus light down to a spot size that is of the order of half or quarter of a wavelength. To focus light down to spot sizes that are of the order of a tenth of a wavelength, near-field transducers (NFTs) are needed.
One approach for directing light onto a storage layer uses a planar solid immersion mirror or lens (PSIM), fabricated on a planar waveguide and a near-field transducer, in the form of an isolated metallic nanostructure placed near the PSIM focus. The near-field transducer is designed to reach a local surface plasmon (LSP) condition at a designated light wavelength. At LSP, a high field surrounding the near-field transducer appears, due to collective oscillation of electrons in the metal. Part of the field will tunnel into an adjacent storage medium and get absorbed, raising the temperature of the medium locally for recording. This design is sensitive of the shape of the NFT, and the location of the NFT in the waveguide. A larger amount of light is absorbed if the isolated near-field transducer is buried in a dielectric of lower thermal dissipation than the medium.